bug#43151: Calibre ebook-viewer requires QtWebEngine

[Andreas Enge]

Hello,

when trying to view an epub using ebook-viewer from the calibre package
(or by directly clicking on an epub in calibre), the program fails with
the message:
   Could not find QtWebEngineProcess

I see that commit d79ec4fd343bc2a72652aa3a4b4ae14bd8df88ac has added
python2-pyqtwebengine and qtwebengine to the calibre inputs, but this
is apparently not enough.

I did not git bisect to see where the problem first appeared, but could
do so if this would help debugging.

Andreas